The present invention relates to a drive system for a covering such as a door, a lid or the like, especially for the lid of a hood receiving compartment of an open car, comprising at least one lifting cylinder which engages on the covering for the purposes of opening and closing, a lock for locking and unlocking the covering, a working cylinder for transferring the lock into a locking position and into an unlocking position, a control valve to which the lifting cylinder is connected via a pressure line, and a control unit for controlling the control valve.
In the Mercedes-Benz SL series, the opening and closing of the hood automatically is undertaken with a hydraulic drive system. In order to close the hood and to move it out of its receiving compartment, it is initially necessary to lift the hood box lid serving as a covering. This hood box lid is locked in its closed position by a mechanical lock actuated by a hydraulic working cylinder. The lifting of the hood box lid is performed by a hydraulic lifting cylinder. An independent control valve is provided for both the working cylinder and the lifting cylinder, with the two being linked by a control device such that the control valve for the movement of the working cylinder to unlock the lock is actuated first, followed by the control valve for the lifting cylinder. The corresponding procedure is followed in reverse for opening of the hood.
DE-PS 925 445 and 48 849 show that in the case of an automatically actuatable hood of a car, it was known initially to swing forward a backrest of a passenger seat before lifting of the hood. The hydraulic cylinders for lifting of the hood and for swinging over of the backrest were linked to each other by a corresponding sequential control. However, no provision was made for a hood box lid which locks a hood receiving compartment and is provided with its own drive system.
An object of the present invention is to improve a covering drive system so that it can be operated with a reduced control effort.
This object has been achieved in accordance with the present invention by arranging the working cylinder in the pressure line. One connection on the working cylinder is connected to the control valve and one connection is connected to the lifting cylinder. Irrespective of the position of the piston of the lifting cylinder and after the transfer of the lock into the unlocking position, the pressure line is released to open the covering.
The result achieved by this measure is that the working cylinder provided for locking is simultaneously used to control the movements of the lifting cylinder. This is advantageous, since the lock of the covering must in any case first be unlocked before lifting of the covering. As a result, the control effort of the drive system is reduced, and an additional control device for the working cylinder is rendered unnecessary.
The control device therefore requires, according to the present invention, only one control valve which triggers a sequential control for the working cylinder and the lifting cylinder.
In the present invention, the working cylinder contains a piston provided with a piston rod connected to the lock. The piston releases, in a position unlocking the covering, a connection of a control line connected to the lifting cylinder. As a result of this additional connection on the working cylinder, the lifting cylinder is actuated to lift the covering as soon as the working cylinder has unlocked the lock on the covering.
In a further embodiment of the present invention, two end switches are connected to the control device to signal a locked and an unlocked end position of the lock. The end switch for signalling the unlocked position of the lock additionally gives a signal for the control of the retaining position of the piston of the working cylinder. The result is to ensure that the connection of the control line on the working cylinder during the lowering movement of the piston of the lifting cylinder remains free, so that the oil thus displaced can flow through the working cylinder.
In a yet further embodiment, a stop is arranged on the piston rod of the working cylinder to actuate the two end switches. As a result, the control unit receives the necessary information, by way of the movement of the working cylinder, in order to initiate a switching-on of the working cylinder.
In a still further embodiment of the present invention, the connection of the working cylinder for the control line is arranged at a distance from a lower stop point of the piston which is somewhat less than the height of the piston, and the distance of the connection from the upper stop point of the piston is greater than the height of the piston. As a result, the piston retains the control line closed in its lower reverse position, but releases it in the region of its upper end position. When the lock is unlocked, the lifting cylinder can thus lift the covering
In another embodiment of the present invention, the piston of the working cylinder is provided with an annular groove from which a return line starts and extends through the piston, terminating in its end face remote from the piston rod and provided with a return valve which is open towards this termination. Consequently, the piston of the working cylinder can be lowered simultaneously with the piston of the lifting cylinder, since the oil displaced in the lifting cylinder can flow through the return line of the working cylinder, which is provided with a return valve. It is thus no longer necessary to have an end switch giving a signal to control the retaining position of the piston of the working cylinder. The piston thus no longer has a locking function so that, for example, an automatically locking lock can be used.